The vast majority of "video formats" like avi, mp4, wmv, mkv, etc. aren't actually video formats. They're just containers which hold a video file, audio file(s), subtitles, chapter indices, etc. all combined into a single file. The video file contained can come in a variety of formats. MPEG4 used to be the common one, but today it's mostly h.264. Newer video files sometimes contains h.265 format video.
So if you've got old video software, it's not uncommon for it to stop working on (say) avi files when it used to work fine with (older) avi files. If it only knows how to read MPEG4 and h.264 video, and the new avi video you're trying to process is h.265, it can't even decode the original video to get started.
If this is the cause...